(1) Field of the Invention
The present invention relates to an apparatus and method for detecting the crank angle of an engine, and more specifically, to a technique for detecting the crank angle of an engine by use of a camshaft sensor and a crankshaft sensor.
(2) Related Art of the Invention
It was common in the prior art to provide to the engine a camshaft sensor for outputting a pulse signal (reference angle signal) at every crank angle corresponding to a control reference position of each cylinder, and a crankshaft sensor for outputting a pulse signal (unit angle signal) at every unit crank angle. In such case, the unit angle signal immediately after the output of the reference angle signal from the camshaft sensor (or the unit angle signal after, by predetermined numbers, the unit angle signal immediately after said output) is set as a control reference position, utilized to control the ignition timing or the fuel injection timing of the engine.
However, according to the prior art method, the permissible divergence in the timing for generating the signal between the camshaft sensor and the crankshaft sensor was only a unit crank angle at maximum. Therefore, in order to detect the reference position with high accuracy while maintaining the angle resolution of the crankshaft sensor, it was either necessary to minimize to the utmost the dispersion caused when manufacturing or mounting the sensor, or it was necessary to perform an individual adjustment operation.
Moreover, if the reference position was to be detected by the signal from the camshaft sensor in an engine equipped with a variable valve device for variably controlling the valve timing of the intake valve by varying the phase of the intake side camshaft with respect to the crankshaft, it was requested that a camshaft sensor be equipped to the discharge side camshaft whose phase will not be changed with respect to the crankshaft. However, in order to detect the phase of the intake side camshaft, it was necessary to provide a camshaft sensor to the intake side camshaft as well, which led to increase in the number of sensors to be mounted, and as a result, raised the manufacturing cost thereof.